Modern automobile engines are generally controlled by a computerized system known as an Engine Control Unit (ECU). To configure the ECU, a single engine or small sample of engines are extensively tested on a dynamometer to establish default control settings for that model of engine. These default values are then applied to the ECUs that are incorporated into the thousands or even millions of subsequently manufactured engines of that model. Among other functions, the default values determine how the ECU will model air flow through the engine.
Many modern vehicles include a system that provides variable valve timing. While different systems exist, each type of system has the ability to alter the opening and closing of intake valves, exhaust valves, or both, to modify the air flow characteristics of the engine. This control over engine air flow allows the engines to run more efficiently and produce fewer emissions by maintaining a predetermined combustion level. In some circumstances the predetermined combustion level may represent optimal combustion conditions but this is not required. The ECU controls the variable valve timing system; therefore, the accuracy of the air flow modeling performed by the ECU is critical to the effective operation of the variable valve timing system.
During the initial dynamometer testing, a specific control parameter known as the mechanical-electrical confidence bit is set in the ECU. The mechanical-electrical confidence bit is assigned one of two possible logical states and represents a fundamental assumption that underlies the air flow modeling performed by the ECU. The first state assumes that the electrical system is perfect, thus all errors are coming from the mechanical system. The second state assumes that the mechanical system is perfect, thus all errors are coming from the electrical system. The ECU models the engine air flow differently depending upon the state of the mechanical-electrical confidence bit and the underlying assumption that the state implies.
Currently, the mechanical-electrical confidence bit is set as a result of the initial dynamometer tests. Such tests are used to determine a default state of the mechanical-electrical confidence bit, which is then applied to all subsequently manufactured engines. In some instances, however, this default state is not the appropriate mechanical-electrical confidence bit state for a particular subsequently manufactured engine. Unfortunately, the default state is used even though an alternate state would provide more accurate air flow modeling and improved performance. An alternate state is a state which is different from the default state. In the example of the mechanical-electrical confidence bit, the mechanical-electrical confidence bit has two values and thus the alternate state is different of the default state. Thus, it is desirable to test the appropriateness of the default state of the mechanical-electrical confidence bit for each engine manufactured and to change the mechanical-electrical confidence bit state when doing so would provide improved performance over the default state.